1. Field of the Invention
The present invention is directed to a system and method for electronically controlling the refrigeration and/or heating of the product storage compartment in a vending apparatus.
2. Related Art
Currently, vending machines have widespread application and utilization. Vending machines can be found not only in restaurants and other eateries, but also both inside and outside such facilities as offices, recreation centers, hospitals, gasoline stations, and apartment complexes. Because of their location, vending machines often experience both high and low levels of usage over a period of time. Further, such machines may be exposed to extremes of temperature and humidity for, extended periods. Some vending machines are run for so long that ice and frost occur in the machines even though the products to be dispensed are warm.
When a vending machine is exposed to extremely cold temperatures, its cooling system should not be running, continuously. In fact, prolonged periods of cold weather can freeze the products in the vending machine.
Moreover, when a vending machine door is open for loading or servicing, continuing to run the machine's compressor may cause problems in normal operation.
In the prior art, various types of systems have been proposed and implemented to optimize vending machine operation under varying conditions. For example, U.S. Pat. No. 5,231,844 to Park discloses a refrigerator defrost control method in which the refrigerator is defrosted by comparing a sensor temperature in the refrigerator with a predetermined temperature during a defrost period. This defrost control method includes sensing the open/closed conditions of the refrigerator doors, and activating a defrost heater when the doors are closed.
U.S. Pat. No. 5,228,300 to Shim discloses an automatic refrigerator operation control method that includes controlling the temperature setting of a chamber; defrost cycling; and the operation of a compressor and fan motor according to the frequency of the door being opened and closed and to the open time of the door.
U.S. Pat. No. 5,046,324 to Otoh, et al. shows a defrosting controller for refrigeration systems. The controller determines a frost melting period from the measurements of the evaporator temperature during defrosting by means of an evaporator temperature sensor.
U.S. Pat. No. 4,932,217 to Meyer shows a process for controlling a heater; particularly, a defrost heater for refrigeration plants. In this process, the temperature of the room to be heated is measured at intervals of time and in each case a measured temperature value is stored.
U.S. Pat. No. 4,916,912 to Levine, et al. shows a heat pump with adaptive frost determination functions.
U.S. Pat. No. 4,903,501 to Harl discloses a refrigerator air-control heated baffle.
U.S. Pat. No. 4,850,198 to Helt, et al. discloses at refrigerator compressor control method involving momentarily energizing the compressor after extended off periods.
U.S. Pat. No. 4,745,629 to Essig, et al. discloses an improved duty-cycle timer that provides a duty-cycle control signal having alternate "on" and "off" intervals of different logic states. In one embodiment of this invention, the duty-cycle timer controls operation of a refrigeration circuit defrost mechanism.
U.S. Pat. No. 3,518,841 to West, Jr. discloses a household refrigerator apparatus that includes an evaporator automatically defrostable through use of an electric heating element energized at varying timed intervals.
In comparison to the present invention, devices and systems known in the prior art, such as those discussed above, do not directly address or solve the problems to which the present invention is directed but rather suffer from those same problems and disadvantages. In particular, conventional refrigeration control systems suffer from unnecessary compressor cycling when the refrigeration system attempts to start before pressures have equalized in the evaporator and the condenser. Also, conventional control systems do not effectively maintain refrigerated compartment temperature when outside temperatures are extremely cold for extended periods. Instead, such system remain unnecessarily idle, with the compressor off, for periods in excess of several hours, thereby allowing ambient conditions to determine the refrigerated compartment temperature. Even further, the conventional refrigeration control systems in the prior art do not provide service personnel any way to efficiently troubleshoot the vending machines.